The two suspects in the Boston Marathon bombings were likely planning other attacks based on a cache of weapons that were uncovered by investigators, Boston’s police commissioner said on Sunday.

Boston Police Commissioner Ed Davis told CBS’ “Face the Nation” that following a firefight between police and the suspects, authorities discovered more homemade explosives, leading them to believe that brothers Tamerlan and Dzhokhar Tsarnaev and were likely planning other attacks.

“We have reason to believe, based upon the evidence that was found at that scene -- the explosions, the explosive ordnance that was unexploded and the firepower that they had -- that they were going to attack other individuals," Davis said. "That's my belief at this point."

Interrogators are waiting to question Dzhokhar Tsarnaev, the surviving suspect in the Boston Marathon bombings, as he remains in hospital in serious condition.

Earlier Sunday, several U.S. media outlets, quoting unnamed sources, said Dzhokhar Tsarnaev was communicating with investigators in writing. Reports indicated he may be unable to speak due to a throat wound.

Dzhokhar Tsarnaev, 19, remained in hospital Sunday, two days after he was pulled from a tarp-covered boat in a backyard in Watertown, Mass. His capture came after a chaotic manhunt that began Friday after his brother, Tamerlan Tsarnaev, died in a gunfight with police.

There is no immediate word on what kind of charges Dzhokhar Tsarnaev may face, but they could be laid as early as Monday, CTV’s Joy Malbon reported.

Dzhokhar Tsarnaev remains under heavy guard in Boston’s Beth Israel Deaconess Medical Center, where 11 victims of the deadly bombings are still being treated.

The Tsarnaev brothers were named as suspects in the bombing attack that killed three and injured more than 180 Monday afternoon near the Boston Marathon finish line.

The most serious charge the teen could face would be the use of a weapon of mass destruction to kill people – a charge that carries a possible death sentence.

An elite interrogation team will question Dzhokhar Tsarnaev without reading him his Miranda rights, which guarantees the right to remain silent and the right to an attorney, U.S. officials said. The exemption is allowed on a limited basis in circumstances where the public may face immediate danger, such as when planted bombs are ready to go off.

American Civil Liberties Union Executive Director Anthony Romero said the exception applies only when the public continues to face a safety threat and is “not an open-ended exception” to the Miranda rule.

The federal public defender’s office has agreed to represent Dzhokhar Tsarnaev once he is charged. Massachusetts public defender Miriam Conrad said the accused should be appointed a lawyer as soon as possible because there are “serious issues regarding possible interrogation.”

But Republican Rep. Mike Rogers told NBC’s “Meet the Press” that he’s not worried about the government decision against reading Dzhokhar Tsarnaev his rights. Rogers said federal agents need to know if there are other bombs out there that the suspect might tell them about.

Rogers, a former FBI agent, said the amount of evidence against Dzhokhar Tsarnaev is so great that a conviction should be easily made.

On Sunday Massachusetts Gov. Deval Patrick said that surveillance video from the bombings show that it is “pretty clear” the level of Dzhokhar Tsarnaev’s involvement. The video shows him dropping his backpack and walking calmly away from it before it explodes.

“It does seem to be pretty clear that this suspect took the backpack off, put it down, did not react when the first explosion went off and then moved away from the backpack in time for the second explosion," Patrick told NBC television.

Also on Sunday, Boston Mayor Thomas Menino told ABC’s “This Week” that it appears that the brothers acted alone.

“All of the information I have is they acted alone,” he said. The Watertown police chief said the same thing on Saturday.

Meanwhile, Republican lawmakers in Washington, D.C., said they suspected the brothers may have been part of a larger conspiracy and criticized the FBI for not investigating Tamerlan Tsarnaev more closely after being advised that he might pose a potential threat in 2011.

“This is the latest in a series of cases like this ... where the FBI is given information about someone as being a potential terrorist," Pete King, the Republican head of the House of Representatives' subcommittee on counterterrorism and intelligence, told "Fox News Sunday."

Boston residents band together

On Sunday, Boston residents gathered for prayer and reflection following the attack.

Photographs of the three people killed in the attack as well as a Massachusetts Institute of Technology police officer killed Thursday were displayed during a service at the Cathedral of the Holy Cross in South Boston.

“I hope we can all heal and move forward,” said Kelly McKernan, who attended the service. “And obviously, the Mass today was a first step for us in that direction.”

Mourners left bouquets of flowers, running shoes and hand-written signs at a makeshift memorial on Boylston Street, near police barriers that cordoned off the crime scene.

Dan Arone visited the site with his wife and infant daughter Sunday, leaving a pair of running shoes at the memorial. The Massachusetts man had crossed the finish line at the Boston Marathon 40 minutes before the bombs went off Monday.

“I thought maybe we’d somehow get some closure,” he told The Associated Press. “But I don’t feel any closure yet.”

Also on Sunday, a five phase plan to return Boylston Street, the site of the bombings, to its original state was introduced.

The plan includes testing the area for remaining biohazards, assessment of the affected buildings and structures and debris removal.

The city is still coming to terms with the chaotic events of the past week.

On Thursday, after discovering a MIT campus police officer shot in his vehicle, police pursued the suspects across the city into the Watertown neighbourhood. Along the way, another officer was wounded and the suspects exchanged gunfire with police and hurled homemade explosives at them.

Police said Tamerlan Tsarnaev ran out of ammunition before police tackled him but while they were handcuffing him, Dzhokhar Tsarnaev drove a hijacked Mercedes SUV at the officers, dragging his older brother’s body down the block. Dzhokhar Tsarnaev eventually fled the scene on foot, while Tamerlan Tsarnaev was taken to hospital where he was later pronounced dead.

Authorities are also trying to determine how the suspects obtained their weapons.

Early on Friday an all-day manhunt for the outstanding Dzhokhar Tsarnaev brought Boston to a virtual standstill, as residents were ordered to stay indoors and public transit was suspended.

He was eventually caught after the order to stay indoors was lifted, and a homeowner discovered the suspect in his boat. The suspect was eventually captured after exchanging gunfire with police.

His capture prompted an outburst of celebration across the city, as residents took to the streets chanting “USA! USA!” and cheering for investigators.

Motive not yet clear

The Tsarnaev family has its roots in Chechnya – a Russian-occupied region that has gone through two wars of independence since 1994.

Investigators have not indicated a possible motive for the Boston attack. However officials and those close to the brothers have painted a picture of the older Tamerlan Tsarnaev becoming increasingly fervent in his Muslim faith and influencing his younger brother.

Two law enforcement officials told the Associated Press that the FBI was informed by the Russian intelligence service in 2011 that Tamerlan Tsarnaev was a follower of radical Islam.

The FBI said its agents interviewed Tamerlan Tsarnaev and relatives but did not find any domestic or foreign terrorism activity.

In an interview with AP, the parents of Tamerlan Tsarnaev said Sunday that the elder brother came to Dagestan and Chechnya for a six-month visit last year but during that time did not associate with Islamic militants in the volatile region of Russia.

The Caucasus Emirate, a group of Islamic insurgents operating in the region, has denied any involvement in the Boston bombings, AP reported.

However, Michael McCaul, chairman of the House homeland security committee, said on CNN’s “State of the Union” that he believes Tamerlan Tsarnaev was radicalized at some point.

“One of the first things he does (upon his return) is put up a YouTube website throwing out a lot of jihadist rhetoric. Clearly something happened, in my judgment, in that six-month timeframe – he radicalized at some point in time. Where was that and how did that happen?”

With files from The Associated Press and The Canadian Press