Ass-ass-in-vestigation

 The word Assassin is an important lead, note the etymology: 

assassin (n.)1530s (in Anglo-Latin from mid-13c.), via medieval French and Italian Assissini, Assassini, from Arabic hashīshīn (12c.), an Arabic nickname, variously explained, for the Nizari Ismaili sect in the Middle East during the Crusades, plural of hashishiyy, from the source of hashish 

Note the following information regarding notable persons on the Nizari Ismaili sect wiki page:  

• Aga Khan IVPrince Karim Al-Husseini (born 13 December 1936)
• Abū Tamīm Maʿad al-Mustanṣir biʾllāh ( 2 July 1029 – 29 December 1094)
• Hasan-i Sabbah ( c. 1050 – 12 June 1124)
• Al-Afdal Shahanshah (1066 – 11 December 1121)
• Abū al-Qāsim Aḥmad ibn al-Mustanṣir (15/16 Sept 1074 – 12 December 1101)

We now have a “December 11, 12, 13(x2), 14,__,  …, 29/Date Sequence” patter cluster. 

On bridging the December 15 gap using the formula: 

• Haris Brkić (July 24, 1974 – December 15, 2000)

My mother passed away on July 23, so his birthday iis meaningful— an addition to the “Off by One” pattern cluster. 

Other notable mentioned on the sects wiki page: 

• Salah ad-Din Yusuf ibn Ayyub^[a] (c. 1137 – 4 March 1193)
• Richard I (8 September 1157 – 6 April 1199),
• Marco Polo (c. 1254 – 8 January 1324)
• Joseph Freiherr von Hammer-Purgstall (9 June 1774 – 23 November 1856)
• Vladimir Alekseevich Ivanow (November 3, 1886 – June 19, 1970) 
• Hasan ibn Ali (c. 625 – 2 April 670)
• Sir Sultan Mahomed Shah (2 November 1877 – 11 July 1957)
• Princess Zahra Aga Khan (born 18 September 1970

My mother’s birthday is November 23.  My stepsons birthday is January 8, and note the “September 18(x2) pattern cluster”. 

The Fidais' apparent lack of fear of personal injury or even death could not be understood by the Crusaders, who propagated the black legends of the so-called Assassins.