Source: Lindsay Lohan lawyer probed for witness tampering March 25, 2013 -- Updated 2138 GMT (0538 HKT) Lindsay Lohan, left, with attorney Mark Heller. Heller is under investigation for suspicion of witness tampering. 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 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. 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. Lindsay Lohan: The reality show we don't want to watch