"He was handcuffed. We don't know how he got the handcuffs free," Patterson said.
It's unclear if Morales' hands were cuffed in front or behind him or if he was shackled. Miami police also declined to speculate on how Morales obtained the object he used to stab the officer. Morales, who was born in Cuba, is believed to have run away.
Morales was sentenced to 10 years in prison in December in Miami after pleading guilty to sexual battery with a deadly weapon, burglary with assault and kidnapping stemming from a 2003 crime. He was being taken to Nevada to serve out life sentences on a separate sexual assault conviction in that state.
Authorities frequently fly inmates across the country and said they are occasionally forced off the plane by an inmate's behavior.
"The airlines are picky," said Miami-Dade Police Deputy Director Juan Perez, who noted airlines will ask officers escorting inmates to leave for minor things because they are worried about liability issues.