James Mulligan, 73, died after being hit by a car as he waited for a bus near his home in High Heworth, Gateshead, in May.

Two youths, who were later arrested, admitted being in the car when Mr Mulligan was knocked-down but escaped prosecution as each blamed each other for being behind the wheel.

Mr Mulligan's family believe the circumstances mean both youths should face charges.

One of these two lads is actually innocent and he's innocent of the most serious offence of causing death by dangerous driving John Platt, solicitor

But the Crown Prosecution Service (CPS) told BBC News Online that in order to prove death by dangerous driving, they have to be able to prove which person was driving the car.

The two youths - aged 18 and 20 - were arrested shortly after the incident, which also injured Mr Mulligan's friend Ivy Clarke, 83.

Mr Mulligan's son, Keith, told BBC Radio Newcastle he was collecting signatures to petition for a change in the law.

"Basically they both admitted being in that car when the accident happened.

"They had fled the scene of the accident, but one was arrested on the day and the other gave himself up the following day.

"When it came down to it, they both blamed each other for driving the car."

Mr Mulligan added: "I started it [the petition] a week-and-a-half ago, we have got over 2,000 signatures and I still have a lot of petition forms out.

Solicitor John Platt told BBC Radio Newcastle it was a rare situation.

"One of these two lads is actually innocent and he's innocent of the most serious offence of causing death by dangerous driving.

"The reason the CPS won't prosecute either of them is because they can't work out, not simply which one is guilty, but which one is not."