In the decade since Sri Lanka’s civil war ended, a former wartime defense chief has successfully dodged accusations of crimes against humanity. He may soon run for president.

But the accusations, which are supported by United Nations inquiries, recently caught up with him in a California parking lot.

The former official, Gotabaya Rajapaksa, oversaw the final stages of a quarter-century-long conflict with Tamil separatists that ended in 2009. So far he has avoided prosecution at home and abroad over the allegations of crimes against humanity.

But in early April, a private investigator tracked Mr. Rajapaksa, now an American citizen, to a Trader Joe’s parking lot in a Los Angeles suburb. He was then personally served with civil court complaints accusing him of a journalist’s murder and the torture of an ethnic Tamil who had Canadian citizenship, court documents show.