LONGMONT, Colo. (CBS4) – Investigators had to don protective suits as they are tried to determine what killed a 6-year-old girl in Longmont Monday morning.

The investigation began at approximately 9 a.m. when the girl, identified as Lluvia Espinoza Morales, was taken to the hospital. She was pronounced dead at the hospital, but there were no signs of foul play.

Police started going down the list of what could have killed the girl. One thought was that she had influenza. Investigators consulted with the Centers for Disease Control and Prevention on how to go into the girl’s home.

“We don’t know the cause. The initial investigation is not showing us anything suspicious,” Cmdr. Jim Lewis with Longmont police said.

Crews in hazmat suits, using all the precautions, entered the girl’s home. Some were also washed down when they were done.

“We don’t know. It could be the flu or it could be something pre-existing,” Lewis said. “But to send our people into an unknown environment and possibly expose them to that would have been irresponsible on our part.”

Neighbor Chloe Dominguez said Morales looked fine when she was outside playing the past few days.