Pope Francis shakes hands with an inmate as he meets with prisoners at Curran-Fromhold Correctional Facility in Philadelphia on Sept. 27, 2015. (Jonathan Ernst/Reuters)

“Dear Carlos,” Pope Francis wrote. “I was pleased to receive your recent letter.”

A pope who has a penchant for surprising personal gestures has done it again — this time by personally replying to an 18-year-old imprisoned in Southern California for involuntary manslaughter in connection with a gang-related killing.

In a year that Francis has declared the Extraordinary Jubilee Year of Mercy, the pope told the prisoner, Carlos Adrian Vazquez Jr., that the “Holy Door to Mercy” is open to him and his fellow convicts.

And on Friday, which begins the third annual Catholic day of prayer called “24 Hours for the Lord,” the Vatican announced a new app that lets anyone seek mercy right from their iPhone.

According to CNN, which reported on Vazquez’s letter from the pope, Francis wrote, “I pray that as you and your fellow residents celebrate the opening of the Holy Door, you may receive these gifts and be filled with peace and hope.”

The letter continued, according to CNN: “Know that the Holy Father is thinking of you and praying for you. And please remember to pray for me, because I greatly need your prayers.”

Vazquez told CNN that he was inspired by a Jesuit priest who works with youths in prison, so he wrote to the pope to ask for forgiveness for his crime. He was sentenced at age 16 to 11 years in detention for his involvement in a gang-related killing. He also wrote a letter to the victim’s family, he said.

“I couldn’t believe it. I didn’t think the pope would write to someone who’s behind bars,” Vazquez said to CNN.

Francis has interacted with prisoners on several occasions in the past. During his visit to the United States in September, he stopped at the Capitol and the White House, but also at a Philadelphia prison.

Francis’s visit to Cuba in September was occasion for the government there to pardon more than 3,500 prisoners. And on his recent trip to Mexico, he planned a stop at a prison in the border city Ciudad Juarez.

Popes have instituted special “jubilee years” for centuries in which Catholics are called to rededicate themselves to prayer. Francis announced that this one — an “extraordinary” year because it falls outside the normal timeline — would focus on mercy, the gift of forgiveness.

The announcements that drew the most attention concerned abortion and the death penalty: During the one-year window, Francis said all priests can “absolve the sin of abortion” for women who have had abortions and wish with “a contrite heart” to again be in the full good graces of the Church.

The pope also urged Catholic leaders not to allow executions in their countries during this year.

And sinners can seek forgiveness on their own smartphones. For the “24 Hours for the Lord,” the Vatican announced the launch Friday of an app called “Click to Pray.”

The app reminds users to pray at three different times of day for specific intentions and lets users ask other people to pray for them.

An initial version in Portugal drew 80,000 users, the Vatican said. On Friday, the app opens up in English, French and Spanish.

One of the first posts in English says, “For my two sons. For Curtis who is a drug addict and for Seth who professes to be an atheist. May our Lord enlighten them.” So far, 24 people have clicked to join the poster, Lisa, in her prayer.

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