A Calgary mother learned a hard lesson Sunday when her unlocked SUV was stolen with her 10-month-old baby son in the back seat.

The woman had stopped at a shopping plaza just before 5:45 p.m. Sunday when she decided to run into the store with her two-year-old. She left her SUV both unlocked and running while her baby son slept in the back seat.

That's when a thief saw his opportunity, jumped into the SUV and took off with the baby in the back.

When the mother returned to find her vehicle gone, she immediately dialled 911. Calgary Police say every available unit within the city that wasn't on a high priority call dropped what they were doing to respond.

For 20 minutes or so, the SUV could not be located and an Amber Alert was in the process of being activated. But then a couple on their way home from dinner spotted a stopped SUV a few blocks away whose driver flagging them down.

The couple pulled over to see if the driver needed help, and after a few minutes of confusion, he asked them to take the baby.

"He in fact asked them to take the baby to the hospital," Calgary Police Insp. Joel Matthews told reporters Sunday night.

The couple called 911. Within minutes, police and EMS arrived on the scene and took the man into custody.

The baby in the back seat was crying but unharmed.

The offender was arrested at the scene.

Killick Donnie Hunter, 21, has been charged with one count each of motor vehicle theft, operating a motor vehicle while unauthorized, and driving while uninsured.

He is scheduled to next appear in court on Feb. 9, 2015.

Calgary Police are reminding drivers to never leave a vehicle with a child inside unattended for any reason -- particularly if the vehicle is running.

With a report from CTV Calgary's Brad MacLeod