London Mayor Sadiq Khan on Tuesday demanded an explanation from the capital’s Metropolitan Police force over how they decided who to fine for events in Prime Minister Boris Johnson’s offices that broke COVID-19 lockdown rules.

New photographs of Johnson at a leaving party in Downing Street in November 2020 were published by ITV News on Monday, reigniting opposition accusations that he breached his own COVID-19 lockdown rules and calls for his resignation.

Johnson was not fined for that gathering, but did receive a fine for another event, a party for his birthday in June 2020.

“Sadiq has today written to the acting Commissioner of the Met to seek a detailed explanation of the factors which were taken into account by investigating officers when decisions were made about whether to take action in individual cases in the Downing Street ‘Partygate’ investigation,” a spokesperson for the mayor said.

“He has asked them to take steps to also reassure Londoners by making this explanation to them directly, because he is concerned that the trust and confidence of Londoners in the police is being further eroded by this lack of clarity.”

Johnson’s spokesman declined to comment directly on the Nov. 13 events, saying the prime minister would answer questions in parliament once a report by senior civil servant Sue Gray into lockdown-breaking events in Downing Street had been published.

Khan’s role as mayor includes oversight of the London police force.

“I do think the photograph that I saw for the first time yesterday will have people across the country scratching their heads how it is that even more fines haven’t been issued,” he told reporters earlier on Tuesday.