Human Rights Watch said the disappearances it had investigated usually followed the same pattern:

“In many cases, these detentions occur in victims’ homes, in front of family members; in others, they take place at security checkpoints, at workplaces or in public venues, such as bars,” the report says. “When victims’ relatives inquire about detainees’ whereabouts at the headquarters of security forces and public prosecutors’ offices, they are told that the detentions never took place.”

Adding to the agony of family members, the prosecutors who are asked to investigate routinely blame the victims, suggesting that they had connections to organized crime or simply ran off for romantic liaisons, the report says. Then they tell the families to conduct searches on their own, sloughing off investigative responsibilities.

When prosecutors do pursue cases, their work is often sloppy. They fail to interview witnesses and suspects, the report says, and don’t bother to visit crime scenes.

Investigators routinely “do not trace victims’ cellphones, track their bank transactions, obtain security camera footage (which is often automatically deleted at regular intervals) or take other time-sensitive actions,” the report says.

Such inaction causes “irreparable loss of information” that could save lives and bring culprits to justice, it added.

“A mother whose son was abducted outside of her home in March 2011 told Human Rights Watch that whenever she met with the investigator in charge of the case, he began their conversation the same way. “He asks me, ‘What new info do you have for me?’ ” the report says.

For relatives of the missing, the searches for their loved ones become “perpetual anguish” that doesn’t end for months or years, or simply remains a wound that doesn’t heal.

The report notes that in at least 20 disappearances of Mexicans in June and July 2011, naval personnel were implicated. The United States works closely with the Mexican navy on drug cases.

In another 13 cases, the Federal Police made the initial arrests. State, local and army units were fingered in the remainder.

In more than 60 cases, security forces appeared to be working in tandem with organized crime groups, it said.

The group cited an incident in late 2011 outside Juarez, in Nuevo Leon state, in which two brothers in the used car business were detained at a police checkpoint. Less than a week later, prosecutors arrested three police officers who “said they had carried out the detention ‘under orders’ of a local crime boss,” the report says.

Human Rights Watch called on Mexico to create “unified, accurate databases of the disappeared,” catalog “unidentified human remains” and try to match the DNA of the remains to those who are missing.

The advocacy group also asked Congress to enact a law that any military or law enforcement agent involved in a disappearance be tried in civilian courts and that suspects not be remanded to military or police holding cells.