After 56-year-old Cesar Sayoc, Jr., was arrested on Friday on the suspicion that he mailed 13 explosives to prominent critics of President Donald Trump, the spotlight turned on a Twitter account that appears to belong to him, which he allegedly used to issue veiled threats to critics of the President. Twitter has apologized for not acting on tweets that clearly violated its terms of conduct.

After the account was surfaced on Friday, Rochelle Ritchie tweeted several screenshots of threatening tweets that @hardrock2016 sent to her. She also posted a screenshot of the Twitter’s response to her report: “we have reviewed your report carefully and found that there was no violation of the Twitter Rules against abusive behavior.”

Hey @Twitter remember when I reported the guy who was making threats towards me after my appearance on @FoxNews and you guys sent back a bs response about how you didn’t find it that serious. Well guess what it’s the guy who has been sending #bombs to high profile politicians!!!! pic.twitter.com/xBY8FMbqnq — R O C H E L L E (@RochelleRitchie) October 26, 2018

Sayoc allegedly used the account to harass numerous others as well — Vice President Joe Biden, former New York attorney general candidate Zephyr Teachout, and New York Times journalist and former Verge writer Sarah Jeong, often with similar threats.

In a series of tweets, @TwitterSafety apologized for not removing tweets sent to Ritchie, saying that “the Tweet clearly violated our rules and should have been removed.” Twitter indicated that it was investigating the lapse and would “continue to work to improve how we handle concerns raised by anyone on Twitter.”

An update. 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. — Twitter Safety (@TwitterSafety) October 27, 2018

We are investigating what happened and will continue to work to improve how we handle concerns raised by anyone on Twitter. — Twitter Safety (@TwitterSafety) October 27, 2018

Twitter responded to The Verge’s questions about what steps it was taking by pointing to two blog posts published earlier this year.

While Twitter did suspend @hardrock2016 after Sayoc was arrested, it comes long after the damage was done. This is a familiar story from Twitter: apologizing for reacting after the fact after it becomes clear that someone violated the site’s terms.

Oh so now you want to suspend his account @Twitter !!! #cesarsayok pic.twitter.com/jgHpPbKDbZ — R O C H E L L E (@RochelleRitchie) October 26, 2018

Update October 27th 11:20AM ET: Updated to include Twitter’s response to a request for comment.