Lindsay Lohan's former assistant failed to show up for a meeting with her prosecutors.

Gavin Doyle - who was with the 26-year-old actress when she crashed into a cement truck on the Pacific Coast Highway last June, to which she pleaded ''no contest'' after being charged for lying to police and trying to blame him - was due to be questioned on Tuesday (19.03.13) as part of an investigation into her lawyer Mark Heller for allegedly witness tampering before her trial on Monday (18.03.13).

A law enforcement source told ''Gavin was supposed to meet with Terry White Tuesday morning to discuss allegations that Lindsay's attorney, Mark Heller, wanted him to change his testimony at Lohan's lying to the cops trial.

''It's been alleged that Heller instructed Doyle to say photographers were chasing the car Lindsay was driving prior to their crash last year -- and that he grabbed the steering wheel, causing Lohan to smash into the cement dump truck. By not showing up for the meeting with White, Doyle isn't doing himself any favours and this makes his behaviour seem very suspicious.

''Terry White is now evaluating what his options are going forward. This will be handled, and at the very least, referred to the New York State Bar, where Heller has a legal license, for further investigation.''

Gavin was expected to be a key witness in Lindsay's trial if it went ahead but was not required to testify against her after she accepted a last minute plea deal to go to rehab for 90 days.