A judge in the southern Spanish city of Granada has charged 10 Catholic priests with sexually abusing altar boys in their care, in a case that has prompted Pope Francis to intervene.

The Pope telephoned one of the victims, who was 14 at the time of alleged abuse, after receiving a personal letter at the Vatican last year. Francis, who has led a wide-ranging crackdown on clerical sexual abuse since becoming Pontiff almost two years ago, apologised to the victim.

He also ordered an internal investigation – a move that prompted the Archbishop of Granada, Francisco Javier Martinez, and fellow priests to publicly prostrate themselves in front of the altar of Granada’s cathedral last November, in a gesture of remorse for failings by the Church.

The judge in the case, Judge Antonio Moreno Marin, published a five-page brief earlier this week after charging the priests. The sordid details of his initial findings make for grim reading, even for those who have dealt with previous abuse cases involving paedophile priests.

The investigation relates to the evidence of one of the altar boys, who claims that he was abused between 2004 and 2007 by a group of priests known as the “Romanones”. The brief states that the boy was 14 when the abuse began and says that the alleged ringleader, Roman Martinez, would invite him and others to a home he owned in Granada.

“When the plaintiff stayed overnight, R. [Roman] proposed sharing a bed even though there were empty ones available. Faced with an initial refusal, R. told him that he was going to sever the father-son-like relationship between them, and the latter consented [...] after feeling physically and psychologically pressured,” Judge Marin says in his briefing.

As time went by, the alleged abuses continued, says the court briefing: at one point the accuser says that Father Roman ordered a massage, when he was “completely naked”. The claimant says that as the requests continued, he complained but was threatened with being dismissed from the church if he did not comply. “I am your father; you have to let yourself go; you are not dealing with your own sexuality properly,” he was allegedly told by the priest.

Father Roman is accused of later trying twice to anally penetrate the victim, while two of the other priests charged by the judge are accused of masturbating the victim, and of “repeatedly [practising] anal and oral sex with R. and with each other” while the claimant was present.

As well as the victim who wrote to Pope Francis, who is not identified in the court documents, others who were also altar boys at the time have supported the claims.

The Catholic Church has defrocked more than 800 priests linked to sex abuse cases in the past decade, and Francis has declared a zero-tolerance stance on the issue.

Despite the Pope’s crackdown, the “Romanones” priests may yet avoid censure. Judge Marin says he considers that there may be a case to answer, but he has allowed the defendants an opportunity to argue that the statute of limitations may apply in the case, since the abuse took place a decade ago. The judge is expected to making a ruling next month.