score:4

Accepted answer

var q =  from i in crimes
    group i by i.Date.ToString("MMM") into grp
    select new {Month = grp.Key, Count = grp.Sum(i => i.Persons)};

score:0

List<Crime>() crimes = ...
var crimesPerMonth = crimes.GroupBy(x => x.Date.Month);

score:11

crimes.GroupBy(c => c.Date.Month)
      .Select(g => new { Month = g.Key, Count = g.Count() });

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