Ratcheting up an investigation that has been criticized by news organizations and press-freedom groups, the San Francisco Police Department said a freelance journalist who had obtained a leaked police report was a suspected “co-conspirator” in the purported “theft” of the document.

The allegation, contained in a statement issued by the Police Department late Tuesday, was the first instance of law enforcement authorities describing the journalist, Bryan Carmody, as a subject of their investigation, according to Mr. Carmody’s lawyer, Tom Burke.

Mr. Carmody has covered news events in the Bay Area — crime scenes, fires, car crashes — for nearly 30 years as a self-employed journalist. In February, he obtained a police report from an unidentified person, or persons, related to the death of San Francisco’s longtime public defender, Jeff Adachi.

[Update: San Francisco police chief apologizes for raid on journalist’s home.]

Mr. Carmody said the document was among the supporting materials he sold to three local news programs that aired reports based on his work the day after Mr. Adachi’s death. Mr. Carmody’s reporting indicated that Mr. Adachi, who was 59 when he died in February, collapsed at the apartment of a woman who was not his wife. (In addition to the police report, Mr. Carmody obtained photographs of the apartment showing alcohol bottles and marijuana gummies.)