7. It is not necessary to refer to all the decisions of this Court articulating the mandate of the Constitution that there is implicit right under Article 21 for speedy trial which in turn encompasses speedy investigation, inquiry, appeal, revision and retrial. To determine whether undue delay has occurred, one must have regard to nature of offence, number of accused and witnesses, workload of the court and the investigating agency, systemic delays. Inordinate delay may be taken as presumptive proof of prejudice particularly when accused is in custody so that prosecution does not become persecution. Court has to balance and weigh several relevant factors. Though it is neither advisable nor feasible to prescribe any mandatory outer time-limit and the court may only examine effect of delay in every individual case on the anvil of Article 21 of the Constitution, there is certainly a need for in-house mechanism to ensure that there is no undue delay in completing investigation. This obligation flows from the law laid down by this Court inter alia in Maneka Gandhi v. Union of India [Maneka Gandhi v. Union of India, (1978) 1 SCC 248] , Hussainara Khatoon (I) v. State of Bihar [Hussainara Khatoon (I) v. State of Bihar, (1980) 1 SCC 81 : 1980 SCC (Cri) 23] , Abdul Rehman Antulay v. R.S. Nayak [Abdul Rehman Antulay v. R.S. Nayak, (1992) 1 SCC 225 : 1992 SCC (Cri) 93] and P. Ramachandra Rao v. State of Karnataka [P. Ramachandra Rao v. State of Karnataka, (2002) 4 SCC 578 : 2002 SCC (Cri) 830] ."