One of Philippine President Rodrigo Duterte’s harshest critics was removed as the chairwoman of the Senate Justice Committee Monday in the midst of an investigation into Duterte’s alleged ties to the extrajudicial killings of drug suspected drug dealers and users.

Senator Leila de Lima last week called a former assassin to testify before her committee. During his testimony, the man, Edgar Matobato, said Duterte ordered the killings of more than 1,000 people and was personally responsible for the murder of at least one man.

On Monday, de Lima’s pro-Duterte colleagues accused her of ruining the country’s reputation with her investigation, and forced her out of her justice committee chairmanship.

The U.S.-based Human Rights Watch group called de Lima’s removal “a blatant and craven move to derail accountability” for the deaths of people killed in Duterte’s war on drugs.

“The Senate is showing greater interest in covering up the allegations of state-sanctioned murder than in exposing them,” it said.

De Lima accused Duterte of being behind her removal. ``I know that the president is behind this,'' she told reporters.

Duterte has also accused de Lima of receiving payments from drug lords, charges she has denied. The Philippines House of Representatives opened hearings into the charges Tuesday.

In an interview with ABS-CBN television, she said she was unsure whether the investigation she launched “will be at all credible” now that she is gone, and warned other senators would likely try to cover up Duterte’s misdeeds.

On Sunday, Duterte asked for a six-month extension for his war on drugs and said the investigations into possible human rights violations would not stop him from continuing to crack down on drug dealers.

“I don't care whether there are a thousand hearings everywhere. I will not stop until the last pushers on the street are fully exterminated,” he said.