Moments after the authorities announced that Luigi Mangione had been arrested in the killing of UnitedHealthcare’s chief executive on Monday, people delved into his digital trail.

Strangers commented on what appeared to be Mr. Mangione’s old Instagram photos from Hawaii and read his reviews of the “Hunger Games” series on Goodreads. Shortly within hours, many of his social media accounts had been scrubbed and were no longer accessible to the public. Others remained active.

Here’s how different social media companies decide whether to scrub a user’s digital footprint.

A digital footprint can suddenly reach a wide audience.

When someone goes from having a private life to getting public attention, online accounts they intended for a small circle of friends or acquaintances are scrutinized by curious strangers — and journalists. (Here are some tips for increasing your online privacy.)

In some cases, these newly public figures or their loved ones can shut down the accounts or make them private. Others, like Mr. Mangione, who has been charged with murder, are cut off from their devices, leaving their digital lives open for the public’s consumption.

Either way, tech companies have discretion in what happens to the account and its content.

Section 230 of the Communications Decency Act protects companies from legal liability for posts made by users. “Companies generally have a lot of freedom to decide what content to allow and what content to remove,” said Jolynn Dellinger, a senior lecturing fellow at Duke Law.

Facebook and Instagram remove ‘dangerous’ individuals.

Meta, the parent company of Facebook, Instagram and WhatsApp, has a “dangerous organizations and individuals” policy that prohibits organizations and individuals from using its platforms if they “proclaim a violent mission or are engaged in violence.” That determination is made on the basis of a user’s online and offline behavior, the policy says.