This same narration is reported from Abd al-Karim, from Ali and Abdullah (may Allah be pleased with them both) and Shurayh (may Allah have mercy on him), that his price is to be paid, even if it exceeds the blood money of a free man.
There is irsal (a break in the chain) between him and Abd al-Karim.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 15959