DETROIT -

Federal authorities are again hoping to jog the memory of the public to drum up tips in the case of a 2011 car bombing that left a lawyer and his two young sons seriously hurt.

The ATF said a radio controlled explosive device, made with parts from a toy car, was attached to Erik Chappell's Volvo station wagon and detonated on Sept. 20, 2011.

Two years ago today Erik Chappell was driving his sons to football practice when a bomb nearly killed all of them.

The device was structured similar to a pipe bomb.

“It’s obviously one thing to have someone target me, but it’s another to have someone target my kids," Chappell said Friday at a press conference in Detroit. “We’re thankful that we get to see them every day."

Chappell, a lawyer, and his sons -- Grant, 15, and Cole, 13 -- had to undergo several surgeries for their injuries, which included broken bones and deep cuts from shrapnel.

Based on the debris found at I-75 and Elm Street in Monroe an ATF explosives expert constructed a mockup of the bomb that was packed with ball bearings and ammunition.

"This was designed with a specific purpose of killing someone," said explosives enforcement officer Michael Eggleston.

The bomb was placed under the vehicle on the passenger side and whoever placed it there used parts from a radio controlled car.

The person in question would have needed access to Chappell's a Volvo and stalked him to learn his patterns.

"It's not overly sophisticated, but you need a good knowledge of electricity. How to make things work," said Eggleston.

Chappell said his family is doing well, both sons are playing football. But, nonetheless, 'We've remained cautious," he said.

He declined to answer questions about whether he had any idea about who may have targeted him or why.

Eggleston explained that whoever designed the device could have detonated it from within about a half a mile.

"They would have been able to see it go off," he said.

Investigators think the parts could have come from an Electrix toy car.

A $20,000 reward is being offered for any tips that lead to an arrest in the case.

Anyone who might have information is asked to call 888-283-2662.