COBB COUNTY, GA - A man already serving time in prison got more time tacked on after threatening to kill an undercover narcotics agent and her family.

42-year-old Alejandra Javier Chaves pled guilty on Monday to two counts of terroristic threats, trafficking methamphetamine, and using a contraband cell phone to orchestrate drug transactions.

In March 2014, Chaves was in the custody of the Georgia Department of Corrections when he used a cell phone smuggled into the prison for drug deals to an undercover narcotics agent in Cobb County.

After two of the delivery people were arrested, authorities said Chaves learned that the buyer in the deal was a sheriff's deputy, then repeatedly threatened to kill the deputy and her family.

"We must protect those who protect us. We will not allow anyone, especially prison inmates, to send poison onto our streets and threaten the lives of our officers or their families," said Deputy Chief ADA Jason Saliba, who prosecuted the case.

Judge Joyette Holmes sentenced Chaves to serve 18 years in prison. He will not be eligible for parole for at least 10 years.