m^4-4m^3+4m^2-9
=m^2(m^2-4m+4)-9
=m^2(m-2)^2-9
=(m^2-2m)^2-3^2
=(m^2-2m+3)(m^2-2m-3)
=(m^2-2m+3)(m-3)(m+1)