Goodwin took the stand for the second day in the trial over the death of father-of-eight Anthony Sergeant in Birmingham in 2018.
The 26-year-old, who suffers with learning difficulties and a low attention span, had a chaperone beside the stand and squeezed a stress reliever before each answer he gave.
He admitted sorting out number plates for one of the cars used in the shooting and claimed he had left his phone on the back seat which accounted for mobile phone cell mast evidence putting him in the car.
He said: "I was at my girlfriend's house, she was due any day so I wanted to be with her.
"I do bad things with cars, sort out number plates and things but I am most definitely not a murderer. I didn't know nothing about no murder. I am a car person not a murder person."
Michael Goodwin and his brother Connor Goodwin, 27, are accused, along with two others, of shooting dead Lea Bank community football manager Anthony Sergeant in 2018.
Anthony Sergeant was shot outside his mother's home in Lea Bank, Birmingham, on August 25, 2018. Another alleged murderer, Dante Mullings, would have been on trial if he had not been shot dead in 2019.
Michael Goodwin admitted asking his brother, who had a number plate machine, to create clone number plates for the red Mercedes used in the shooting. But claimed he left his phone in the car on the night of the killing, and that Mullings gave a mutual friend the phone to give to him that night.
He said: "I had been looking round alleyways for my phone, and was just happy to have it back because I did not have to buy a new one."
Connor Goodwin, 27, and Michael Goodwin, along with Leon Riley, 21, of Bridgelands Way, Perry Barr, and Keenan Anderson, 25, of Albert Road, Handsworth, are all accused of murder, which they deny.
All deny murder and the trial continues.