Commercial filming near the Hollywood sign requires multiple permits and licences from different bodies in Los Angeles.
Zarrinnam tells BBC Newsbeat Sweeney and her crew had permits to film within the city and Griffith Park, where the sign is located, but did not have permission from the trust to enter the fenced-off area around it.
And the Hollywood Chamber of Commerce (HCoC), which owns image rights to the sign, says it did not issue a licence for the production.
Zarrinnam says he is conducting his own investigation into what happened, but has yet to receive a reply from Sweeney or her production company.
“I have to be fair,” he says.
He says the fact some permits had been obtained leaves the possibility that those involved may genuinely have believed the project was authorised.
“Sydney Sweeney probably isn’t reading paperwork,” he says.
“Did she think she had the right to do that? Did her production team tell her what the do’s and don’ts were?”