The director of the Reston Zoo, who is accused of mistreating a sick wallaby, had told investigators that she humanely euthanized the animal, according to court papers.

Meghan Morgensen, 26, of Silver Spring was arrested on Friday and charged with animal cruelty and possession of a controlled substance, after a five-month investigation into improper treatment of injured animals and improper use of euthanasia drugs at the zoo, police said.

In late January, police received a tip from a worker at the zoo who told investigators that he or she captured the injured wallaby, examined it, made recommendations for its treatment and notified Morgensen, according to a search warrant.

The employee left the zoo to get supplies, but when he or she returned the wallaby was gone, according to the search warrant. The employee found the wallaby’s crate next to a five-gallon bucket of water and the wallaby’s body was in a trash bag in a dumpster nearby, according to the search warrant.

The worker confronted Morgensen and resigned from the zoo job.

A Fairfax County animal control officer met with Morgensen a short time later, according to the search warrant. She told the investigator that she euthanized the wallaby by injecting it with a well-known drug used for that purpose, but the officer found no sign of an injection on the wallaby’s body.

Another informant later told police that Morgensen allegedly had a history of drowning animals at the zoo, according to the search warrant.

Police said the investigation into the case is ongoing and detectives think Morgensen received instruction on how to euthanize the wallaby from the zoo’s corporate director, according to the search warrant.

Morgensen did not return a call to the zoo on Monday.