Out of interest did a search to see how they were covering it. Three results for 'Starobilsk' (presumably the Ukrainian spelling). The headlines tell their own story:

'Rosenberg: Luhansk strike sparks Russian accusations and vow to retaliate' - https://www.bbc.co.uk/news/articles/cvgz05jyrrpo
'Putin vows retaliation after accusing Ukraine of hitting student dormitory' - https://www.bbc.co.uk/news/articles/c5y74lwx395o
'Large-scale Russian attack on Ukraine leaves four dead and dozens injured' (mentioned in passing) - https://www.bbc.co.uk/news/articles/clyp6831yp5o
'Russia ramps up threats against Ukraine. What does that say about the war?' (mentioned in passing) - https://www.bbc.co.uk/news/articles/c3v22ylzpqzo

All very keen to stress claims from Ukrainian sources that it was a genuine military target, skeptical about casualty reports, dismissive of Russian officials calling it a terrorist attack, careful to note that Russia allegedly perpetrates similar attacks on Ukraine every day etc etc.

Contrastingly a search for 'mariupol theatre' turns up 23 results with headlines like the following, all presumably given much greater prominence on the website:

'Mariupol theatre: 'We knew something terrible would happen' ' - https://www.bbc.co.uk/news/world-europe-60776929
'A bomb hit this theatre hiding hundreds - here's how one woman ...' - https://www.bbc.co.uk/news/world-europe-60835106
'Russia's attack on Mariupol theatre a clear war crime, Amnesty says' - https://www.bbc.co.uk/news/world-europe-61979873
'War in Ukraine: Estimated 300 dead in Mariupol theatre strike' - https://www.bbc.co.uk/news/world-europe-60873435
'Mariupol theatre demolished 'to hide Russian crimes', aide says' - https://www.bbc.co.uk/news/world-europe-64075088

etc etc...

The claim of 300 dead (some media orgs went with 600, eg: https://apnews.com/article/Russia-ukraine-war-mariupol-theater-c321a196fbd568899841b506afcac7a1 ) was quietly revised downwards by Amnesty a few months later to 'at least a dozen', hastening to add 'and likely many more':

'This estimate is lower than previous counts, reflecting the fact that large numbers of people had left the theatre during the two days prior to the attack, and most of those who remained were in the theatre’s basement and other areas that were protected from the full brunt of the blast.'

Though this didn't prevent the conclusion that it was 'a deliberate air strike targeted at a civilian object' and that:

'“After months of rigorous investigation, analysis of satellite imagery and interviews with dozens of witnesses, we concluded that the strike was a clear war crime committed by Russian forces,” said Agnès Callamard, Amnesty International’s Secretary General.

“Many people were injured and killed in this merciless attack. Their deaths were likely caused by Russian forces deliberately targeting Ukrainian civilians.

“The International Criminal Court, and all others with jurisdiction over crimes committed during this conflict, must investigate this attack as a war crime. All those responsible must be held accountable for causing such death and destruction.”' - https://www.amnesty.org/en/latest/news/2022/06/ukraine-deadly-mariupol-theatre-strike-a-clear-war-crime-by-russian-forces-new-investigation/

We await their verdict on the Starobelsk strikes...

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