LAS VEGAS - Philippine National Police Chief Ronald "Bato" dela Rosa has ordered an investigation into the death of Albuera, Leyte Mayor Ronald Espinosa, promising that there would be no cover-up in the process.

In a phone interview with ABS-CBN News, dela Rosa said he ordered a police probe into the circumstances surrounding Espinosa's death, including why a warrant was needed to look inside his jail cell.

Espinosa was shot dead inside his cell at the Baybay City Provincial Jail in Leyte on Saturday morning. Authorities said the mayor fired shots at them, forcing them to fight back.

Dela Rosa said one of the angles that he is looking into is the alleged blue book that Espinosa's son, Kerwin, is holding.

The book allegedly contains names of police officials involved in the protection of the illegal drug trade.

The police chief added that he respects Senator Panfilo Lacson's opinion but appealed that the senator wait for investigation results first.

Lacson said the death of Espinosa smelled of an "EJK" or extra-judicial killing, citing allegedly questionable circumstances in the incident.

Dela Rosa, who is in Las Vegas on official leave, is set to watch Senator Manny Pacquiao's boxing match against Jesse Vargas with his family.

But he said he did not spend any of his personal money on the trip because Pacquiao, who invited him, paid for everything from the tickets to his hotel and even allowance.- With reports from Jeff Canoy, ABS-CBN News