PALO ALTO — A man employed by a private security firm to watch for suicidal people on the Caltrain tracks has been arrested for alleged criminal conduct, bringing the total number of guards who have reportedly run afoul of the law to four.

On Monday, Palo Alto police arrested Luke Ryan Sauer, 35, of San Carlos, on a misdemeanor warrant for lewd conduct.

The case began around 6:45 p.m. Feb. 21, when an officer went to check on a man slumped over inside a white 2001 Chrysler Sebring parked on the 4000 block of Park Boulevard, according to police.

Police said Sauer was dressed in his Track Watch uniform and talking on his cellphone.

The officer did not directly witness a lewd act but concluded that Sauer had been masturbating, according to police. A report was submitted to the Santa Clara County District Attorney’s Office, and on March 9, a single misdemeanor count of lewd conduct was filed against Sauer.

Police said Sauer was arrested without incident around 6:20 p.m. Monday on the first block of James Avenue in Redwood City and booked into the Santa Clara County main jail in San Jose.

Sauer is the fourth guard to reportedly run afoul of the law.

In October, James Chester Broughton was arrested on suspicion of burglarizing three homes in Palo Alto. Police also arrested Kenneth White near his post for a bench warrant involving petty theft from a Fry’s Electronics in San Jose. Another guard, Brett Scott, faces drug charges in Palo Alto.

According to an NBC Bay Area investigation, the men were employed by Val Security Inc., which the city hired to keep tabs on the Caltrain tracks following a teen suicide cluster in 2009-10. A second cluster in 2014-15 led to an expansion of the Track Watch program.

Capping a search that began the previous spring for a firm that could provide guards nearly 24 hours a day, the Palo Alto City Council voted in November to hire Cypress Security LLC, Sauer’s employer.

Police said Cypress immediately suspended Sauer after being told about the alleged incident in February and promised he would not work another shift in the city during the seven-month, $439,442 contract.

Anyone with information about the case can call Palo Alto’s 24-hour dispatch center at 650-329-2413. Anonymous tips can emailed to paloalto@tipnow.org or sent via text message or voice mail to 650-383-8984.

Staff writer Jacqueline Lee contributed to this report. Contact Jason Green at 408-920-5006. Follow him at Twitter.com/jgreendailynews.