BART has a crime problem, and the agency is doing its best to hide it. Two teen swarm attacks in three months at the same station have yielded no public warnings and little notice, only the barest of bureaucratic posting.

With robberies rising on the mainstay commute system, there needs to be clear notice and advice to riders concerned about safety. Police announcements, requests for witnesses and public warnings are missing. Passengers aren’t clued in on the extent of the problem or what they can do to protect themselves and help authorities.

The latest incident involved a group of some 10 teen robbers who grabbed an iPhone 7 from a female passenger and fled the train at the Coliseum Station. An off-duty 62-year-old security guard spotted the trouble, pursued the pack and retrieved the device. His good citizen actions are praiseworthy, as was the quick work by BART police who caught up with the alleged attackers. They were detained, photographed and released with future charges a possibility.

Word of the attack, however, didn’t filter out for days. That’s also what happened in April when a larger mob of 40 youths jumped fare gates and swept aboard a BART car at the same station. They roughed up and robbed riders before taking off. Two suspects were later arrested and charged with undisclosed offenses.

In the April incident, a bare-bones summary was included in a police log emailed to reporters who had signed up for such notices, a procedure that drew little notice until a Chronicle staffer reported the attack. Afterward, that unsatisfactory process was overhauled, putting all BART crime reports on a public website, CrimeMapping.com. But the new practice understates the extent of the incident and does little to warn passengers or solicit public help.

The two attacks aren’t isolated. Robberies aboard BART trains climbed 45 percent in the past year. In the first three months of this year, there were 71 incidents, compared with 49 in the same period the year before.

BART is taking steps to address the problem, ranging from full installation of surveillance cameras aboard each car to increased patrols by the transit agency’s police force. These are positive pushes in reducing crime and tracking lawbreakers.

But the public isn’t getting the full story on the extent of the problem and what they can do. Muffling crime reports poorly serves riders who need to know more to protect themselves and other commuters. BART is a vital service that hundreds of thousands of riders depend on. They aren’t getting the full protection they deserve.