"The investigation of the 52 fires believed connected to this defendant is not over," Cooley said in a statement.
Authorities said they believed he was angry over his mother's legal troubles and went on a nighttime rampage of burning parked cars a day after she appeared in court last week.
Burkhart has been put on suicide watch, a law enforcement official said Wednesday. The official spoke on condition of anonymity because of privacy issues.
Burkhart's mother, Dorothee Burkhart, said in court Tuesday that her son was mentally ill.
Harry Burkhart is also under investigation in his home country of Germany for a house fire north of Frankfurt days before he traveled to the United States in October.
The fire at the house, which belonged to the Burkhart family, has been ruled an arson, Marburg prosecutors' spokeswoman Annemarie Wied said Wednesday.
Burkhart did not live in the area, but his name surfaced as a suspect after he filed an insurance claim shortly after the fire, Wied said.
Burkhart, whom Wied identified only as "Harry B." in keeping with German privacy laws, has not been questioned in the case and no arrest warrant has been issued for him. She said she did not know how long ago he had been identified as a suspect in the arson investigation.
Court documents were unsealed Tuesday that revealed Dorothee Burkhart is charged in Germany with 19 counts of fraud, including failing to pay for a 2004 breast-augmentation surgery and pilfering security deposits from renters.