A judge has declared a mistrial over whether a German man was sane when he set dozens of fires across Los Angeles during three nights of terror nearly five years ago.

Jurors deadlocked Friday in the sanity phase of Harry Burkhart's trial.

The same jury previously found the former Frankfurt resident guilty of nearly 50 arson counts for fires he set around New Year's 2012.

Prosecutors say Burkhart burned cars and homes to avenge his mother's extradition to Germany on fraud charges. They say the 29-year-old threatened to "roast America" and would have continued if he hadn't been caught.

No one was seriously injured during the fires that caused an estimated $3 million in damage, but the blazes ignited widespread fear.

Burkhart's attorney argued his client was seriously mentally ill.