Los Angeles ( CNN ) -- The lawyer who represented Lindsay Lohan in her lying-to-cops case last week is under investigation for suspicion of witness tampering , a source close to the investigation said Monday . Santa Monica police are investigating New York lawyer Mark Heller on suspicion of asking Lohan 's personal assistant , who was in the car with the actress when she was involved in a car crash last June , to lie in his testimony by saying he had control of the Porsche when it crashed into a dump truck , the source said . The Santa Monica city attorney asked the city 's police to investigate , according to the source , who asked not to be identified since the source is not authorized to discuss it with news media . Photos : Celebrity mugshots . `` I can sum it up in one word : ridiculous , '' Heller said when asked for a comment . `` What can I tell you ? '' Heller was in a Los Angeles courtroom with Lohan , 26 , last week when she agreed to enter a no-contest plea on the charges of misdemeanor charges of lying to police , reckless driving and violating her probation for shoplifting conviction . The judge sentenced Lohan to 90 days in a `` locked in '' drug rehab facility in lieu of a 90-day jail term . Her probation was also extended by two years . Her father , Michael Lohan , accused Heller of unethical and criminal conduct in his representation of his daughter after last week 's hearing , saying prosecutors were investigating Heller for tampering with `` a star witness . '' Lindsay Lohan : Keep me on set , it 's safer that way . Lohan hired Heller to replace Shawn Holley , the Los Angeles lawyer who represented the actress in dozens of court appearances over the past several years . She 's spent 250 days in five rehab facilities since January 2007 , including one long court-ordered stint after a failed drug test . The actress has appeared in court at least 21 times before four Los Angeles judges who have now found her in violation of probation six times and sentenced her to a total of nine months in jail . Lohan has spent about two weeks behind bars in six trips to the Los Angeles County jail , served 35 days under house arrest and worked about 67 days of community service at the county morgue . Lindsay Lohan : The reality show we do n't want to watch .
Santa Monica city attorney asked police to investigate Mark Heller , a source says . `` I can sum it up in one word : ridiculous , '' Heller says about probe report . Lohan avoided trial by pleading no contest to lying to cops about a car crash . Lohan hired New York lawyer Heller to replace her longtime lawyer Shawn Holley .