Cesar A. Sayoc, the man suspected of sending potential pipe bombs to a number of high-profile Democratic leaders, reportedly frequently threatened violence on his Twitter TWTR, +1.62% account.

A Twitter account with the handle @hardrock2016 appears to belong to Sayoc, 56, bearing many photos of his likeness, including one of him holding a sign attacking CNN — one of the organizations he stands charged with having mailed a pipe bomb to this week.

Rochelle Ritchie, a Democratic strategist and media commentator, said she reported the @hardrock2016 account to Twitter after threats against her following her appearance on Fox News FOX, +2.13% in early October.

Twitter declined to take action, saying “there was no violation of the Twitter Rules against abusive behavior,” according to a screen shot Ritchie shared online Friday.

Twitter released a statement Saturday: “We made a mistake when Rochelle Ritchie first alerted us to the threat made against her. The Tweet clearly violated our rules and should have been removed. We are deeply sorry for that error.”

The company has been under fire for its handling of abusive behavior on its platform. The company’s user base has declined by 326 million monthly users in the past quarter after it purged fake and malicious accounts en masse as a means to address the criticism.

Compared with the year-earlier quarter, sales grew 29% to $758 million in the third quarter, above analyst expectations of $701 million.

Twitter’s rules state that abuse is not tolerated but that “context matters” when evaluating what constitutes abuse. Factors considered include whether “the behavior is targeted at an individual or group of people; the report has been filed by the target of the abuse or a bystander; the behavior is newsworthy and in the legitimate public interest.”

Enforcement of Twitter’s rules varies widely. In August, Twitter banned right-wing conspiracy theorist Alex Jones from Twitter for violating its rules by allegedly encouraging violence, telling his followers on Twitter to “get their weapons ready.”

In October 2017, some women called for a boycott of Twitter to show solidarity with the “victims of hate and harassment [whom] Twitter fails to support” after Twitter suspended the account of actress Rose McGowan for sharing a private phone number in a tweet.

Activists have called for more targeted abuse-prevention tools from the app, including advanced block options that would allow users to share lists of people they have blocked so that groups of harassers cannot target multiple accounts.

In 2017, Twitter added a tool that collapses abusive or low-quality tweets in replies and allows accounts to block replies from non-verified users. It also created a technology for limiting an abusive account’s audience, known as “shadow banning,” that temporarily makes a user’s activity viewable in fewer feeds.

Still, reports can easily slip through the cracks. A 2017 Buzzfeed report found Twitter failed to block users for clear and credible threats of violence on many occasions.